LOS ANGELES — The last and strongest of three storms to hit Southern California this week slid into the region Thursday, generating periods of heavy rain, which could trigger street flooding and shallow mud and debris flows in several areas previously denuded by wildfires, National Weather Service forecasters said.

The rain could unleash mudslides and debris flows “in and near recent burn scars across Los Angeles, Ventura, and Santa Barbara Counties. These include the Hill, Sherpa, South, Stone, Thomas, Whittier and Woolsey burn scars,” according to an NWS statement.

As the rain continued Thursday morning, the northbound 101 Freeway was closed at the I-10/Seventh Street interchange near downtown due to flooding in the tunnel.

The strong wind catches a woman’s umbrella as she walks along the beach just north of the Huntington Beach Pier in Huntington Beach on Thursday morning, January 17, 2019, as another storm brought more rain to Orange County and Southern California. (Photo by Mark Rightmire, Orange County Register/SCNG)

A kitesurfer took advantage of the high winds to ride the waves just north of the Huntington Beach Pier Rain in Huntington Beach on Thursday, January 17, 2019, as another storm brought more rain Orange County and Southern California.
(Photo by Mark Rightmire, Orange County Register/SCNG)

Armed with an umbrella, a woman walks along the beach just south of the Huntington Beach Pier in Huntington Beach on Thursday morning, January 17, 2019 as another storm brought more rain to Orange County and Southern California. (Photo by Mark Rightmire, Orange County Register/SCNG)

A man gives a thumbs-up as he passes others braving the wind and rain as they walk on the Huntington Beach Pier in Huntington Beach on Thursday, January 17, 2019, as another storm brought more rain to Orange County and Southern California. (Photo by Mark Rightmire, Orange County Register/SCNG)

A kitesurfer took advantage of the high winds to ride the waves just north of the Huntington Beach Pier Rain in Huntington Beach on Thursday, January 17, 2019, as another storm brought more rain Orange County and Southern California.
(Photo by Mark Rightmire, Orange County Register/SCNG)

It was more rain and wind early on Thursday morning, January 17, 2019, as these people cross Ocean Avenue in Seal Beach while another storm continued to soak Orange County. (Photo by Mark Rightmire, Orange County Register/SCNG)

A lone beach goer stops and stares out into the ocean just north of the Huntington Beach Pier in Huntington Beach on Thursday morning, January 17, 2019, as another storm brought more rain to Orange County and Southern California.
(Photo by Mark Rightmire, Orange County Register/SCNG)

The weather service at 5:40 a.m issued a flood advisory for most of LA County and eastern Ventura County and said it would expire at 8:30 a.m. This was in response to Doppler radar and rain gauge indications that widespread moderate rain was falling, “with numerous embedded heavy showers.”

Later, the weather service extended the flood advisory until 10:30 a.m.

Rainfall rates were highly variable but generally averaged .15 to .30 inches per hour, with up to .50 inch per hour in some areas.

“The rain will cause widespread ponding of water on area roadways through the morning commute with flooding of low lying areas,” warned an NWS statement.

Also in LA County, a flash flood watch will be in force until 1 p.m. Thursday along the coast, in the Santa Monica Mountains Recreational Area, the San Gabriel Mountains, the San Fernando and Santa Clarita valleys, beach cities, Long Beach, Beverly Hills and Hollywood. In all, it covers the Woolsey, Hill, South, and Stone burn scars in Los Angeles and eastern Ventura Counties, the NWS said. Forecasters say they expect peak rainfall rates of between a half-inch and three quarters of an inch of rain per hour in the watch zone.

“Rainfall of this intensity can produce shallow mud and debris flows in and near recent burn areas. In addition, localized flooding is possible across other parts of Los Angeles and Ventura Counties, along with rockslides and mudslides that could produce road closures,” according to the NWS statement.

“A flash flood watch means that conditions may develop that lead to flash flooding. Flash flooding is a very dangerous situation,” said the NWS, adding that Southern California residents in or below the recently burned areas are urged to take the steps necessary to protect their property. Persons in the watch area should remain alert and follow directions of emergency preparedness officials.”

A rockslide prompted the closure of Topanga Canyon Boulevard between Pacific Coast Highway and Grand View Drive, according to the Los Angeles County Sheriff’s Department. Other closures include Malibu Canyon Road between Piuma and Mailbu Knolls and Decker Road between Mulholland Highway and PCH. A portion of La Tuna Canyon in Sun Valley was closed because of a rock slide Wednesday night, but has since reopened.

A tree fell along Lookout Mountain Avenue in the Hollywood Hills, knocking out power to 300 customers, according to a Los Angeles Department of Water and Power outage map. Repair crews were working to clear the tree and restore power.

Along the coast, an extended period of high surf is expected through Friday, the NWS said. A high surf advisory will be in effect in LA County until 2 p.m. Thursday, followed by a less serious high surf warning from 2 p.m. Thursday until 9 p.m. Friday.

Breaking waves of 5 to 8 feet will pound the shore through this morning, then increase to 6 to 10 feet, then 10 to 15 feet Friday morning, according to an NWS statement.

Amid the high surf, ” there is an increased risk for ocean drowning. Rip currents can pull swimmers and surfers out to sea. Large breaking waves can cause injury, wash people off beaches and rocks and capsize small boats near shore,” warned an NWS statement. Moderate coastal flooding is possible over low-lying coastal areas including beaches, beach parking lots and harbor walkways, and with vulnerable coastal roadways during the highest surf and tides.”

Off the coast, a gale warning expired at 3 a.m. Thursday, and a small craft advisory will follow suit at 9 a.m.

In the San Gabriel Mountains and the Antelope Valley, a wind advisory will be in effect until 3 p.m. Thursday. Winds of 20 to 35 mph are expected, along with gusts of up to 55 mph.

“Gusty winds will make driving difficult, especially for high-profile vehicles,” warned the NWS, saying that driving will be particularly difficult on Interstate 5 and Highways 14 and 138, especially for high profile vehicles.

The NWS forecast rain in LA County Thursday and highs of 52 degrees on Mount Wilson; 57 in Palmdale and Lancaster; 59 in Santa Clarita; 60 in Avalon, Pasadena and San Gabriel; 61 in Burbank; 62 in downtown LA, Long Beach, Woodland Hills and at LAX. A mix of partly cloudy and sunny days are forecast over the next six days.

In Orange County , showers were forecast Thursday, along with highs of 48 on Santiago Peak; 55 on Ortega Highway at 2,600 feet; 58 in Fremont Canyon; 60 in Yorba Linda; 61 in Laguna Beach and San Clemente; 62 in Anaheim and Mission Viejo; and 63 in Newport Beach, Fullerton and Irvine. Orange County will also experience a mix of partly cloudy and sunny skies over the next six days.

Join the Conversation

We invite you to use our commenting platform to engage in insightful conversations about issues in our community. Although we do not pre-screen comments, we reserve the right at all times to remove any information or materials that are unlawful, threatening, abusive, libelous, defamatory, obscene, vulgar, pornographic, profane, indecent or otherwise objectionable to us, and to disclose any information necessary to satisfy the law, regulation, or government request. We might permanently block any user who abuses these conditions.

If you see comments that you find offensive, please use the “Flag as Inappropriate” feature by hovering over the right side of the post, and pulling down on the arrow that appears. Or, contact our editors by emailing moderator@scng.com.